- needs two copies of gene to express phenotype- 50% M 50% F- may have ethnic predisposition (sickle cell and CF)- transmittance not usually observed, may have no family history- less variance- full penetrance- consanguinity can increase the probability of - no family history, dot on the map (only one generation affected)

- F: both X mutated || M: singular X mutated- much more common in M than F (though F is observed)- can be inherited through several generations, male to male transmittance never observed- all daughters of affected M are carriers- F carriers may have mild expression- only M, no M to M transmission

- F: only one X mutated || M: singular X mutated- much more common in F than M (though M is observed, often lethal)- Male to Male transmission is not observed- daughters of affected M will always be affected- affected M gives to all daughters- extremely rare!!!